System for additively manufacturing composite structure

ABSTRACT

A system for additively manufacturing a composite structure is disclosed. The system may include a support, and a print head operatively connected to and moveable by the support. The print head may be configured to discharge a continuous reinforcement that is at least partially coated in a liquid matrix. The system may also include a cure enhancer connected to the print head and configured to expose the discharge to cure energy to cause the, and a controller in communication with the heater and the cure enhancer. The controller may be configured to selectively activate the heater and the cure enhancer.

RELATED APPLICATION

This application is based on and claims the benefit of priority fromU.S. Provisional Application No. 62/797,078 that was filed on Jan. 25,2019, the contents of which are expressly incorporated herein byreference.

TECHNICAL FIELD

The present disclosure relates generally to a manufacturing system and,more particularly, to a system for additively manufacturing compositestructures.

BACKGROUND

Continuous fiber 3D printing (a.k.a., CF3D®) involves the use ofcontinuous fibers embedded within a matrix discharging from a moveableprint head. The matrix can be a traditional thermoplastic, a powderedmetal, a liquid resin (e.g., a UV curable and/or two-part resin), or acombination of any of these and other known matrixes. Upon exiting theprint head, a head-mounted cure enhancer (e.g., a UV light, anultrasonic emitter, a heat source, a catalyst supply, etc.) is activatedto initiate and/or complete curing of the matrix. This curing occursalmost immediately, allowing for unsupported structures to be fabricatedin free space. When fibers, particularly continuous fibers, are embeddedwithin the structure, a strength of the structure may be multipliedbeyond the matrix-dependent strength. An example of this technology isdisclosed in U.S. Pat. No. 9,511,543 that issued to Tyler on Dec. 6,2016 (“the '543 patent”).

Although CF3D® provides for increased strength, compared tomanufacturing processes that do not utilize continuous fiberreinforcement, improvements can be made to the structure and/oroperation of existing systems. For example, Applicant has found thatconditioning the matrix prior to discharge can improve the fabricationprocess and enhance properties of the resulting structure. The disclosedadditive manufacturing system is uniquely configured to provide theseimprovements and/or to address other issues of the prior art.

SUMMARY

In one aspect, the present disclosure is directed to a system foradditively manufacturing a composite structure. The system may include asupport, and a print head operatively connected to and moveable by thesupport. The print head may be configured to discharge a continuousreinforcement that is at least partially coated in a liquid matrix. Thesystem may also include a cure enhancer connected to the print head andconfigured to expose the discharge to cure energy to cause the, and acontroller in communication with the heater and the cure enhancer. Thecontroller may be configured to selectively activate the heater and thecure enhancer.

In another aspect, the present disclosure is directed to a method ofadditively manufacturing a composite structure. The method may includereceiving a liquid matrix into a print head, receiving a continuousreinforcement into the print head, and at least. The method may alsoinclude selectively discharging the continuous reinforcement and theliquid matrix only when a temperature of the liquid matrix is within adesired range.

In yet another aspect, the present disclosure is directed to anothermethod of additively manufacturing a composite structure. This methodmay include receiving a liquid matrix into a print head, receiving acontinuous reinforcement into the print head, and at least partiallycoating the continuous reinforcement with the liquid matrix inside ofthe print head. The method may also include monitoring a temperature ofthe liquid matrix inside of the print head, and responsively adjustingthe temperature of the liquid matrix. The method may further includeselectively discharging the continuous reinforcement and the liquidmatrix when a temperature of the liquid matrix is within a desiredrange, and exposing the liquid matrix after discharge.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of an exemplary disclosed additivemanufacturing system;

FIG. 2 is an enlarged isometric illustration of an exemplary disclosedportion of the additive manufacturing system of FIG. 1; and

FIG. 3 is a flowchart depicting an exemplary disclosed method that maybe performed by the additive manufacturing system of FIG. 1.

DETAILED DESCRIPTION

FIG. 1 illustrates an exemplary system 10, which may be used tomanufacture a composite structure 12 having any desired shape. System 10may include a support 14 and deposition head (“head”) 16. Head 16 may becoupled to and moved by support 14. In the disclosed embodiment of FIG.1, support 14 is a robotic arm capable of moving head 16 in multipledirections during fabrication of structure 12. Support 14 mayalternatively embody a gantry (e.g., an overhead bridge or single-postgantry) or a hybrid gantry/arm also capable of moving head 16 inmultiple directions during fabrication of structure 12. Although support14 is shown as being capable of 6-axis movements, it is contemplatedthat support 14 may be capable of moving head 16 in a different manner(e.g., along or around a greater or lesser number of axes). In someembodiments, a drive may mechanically couple head 16 to support 14, andinclude components that cooperate to move portions of and/or supplypower or materials to head 16.

Head 16 may be configured to receive or otherwise contain a matrix(shown as M in FIG. 2). The matrix may include any type of material(e.g., a liquid resin, such as a zero-volatile organic compound resin, apowdered metal, etc.) that is curable. Exemplary resins includethermosets, single- or multi-part epoxy resins, polyester resins,cationic epoxies, acrylated epoxies, urethanes, esters, thermoplastics,photopolymers, polyepoxides, thiols, alkenes, thiolenes, and more. Inone embodiment, the matrix inside head 16 may be pressurized (e.g.,negatively and/or positively), for example by an external device (e.g.,by an extruder, a pump, etc.—not shown) that is fluidly connected tohead 16 via a corresponding conduit (not shown). In another embodiment,however, the pressure may be generated completely inside of head 16 by asimilar type of device. In yet other embodiments, the matrix may begravity-fed into and/or through head 16. For example, the matrix may befed into head 16, and pushed or pulled out of head 16 along with one ormore continuous reinforcements (shown as R in FIG. 2). In someinstances, the matrix inside head 16 may need to be kept cool and/ordark in order to inhibit premature curing or otherwise obtain a desiredrate of curing after discharge. In other instances, the matrix may needto be kept warm and/or illuminated for similar reasons. In eithersituation, head 16 may be specially configured (e.g., insulated,temperature-controlled, shielded, etc.) to provide for these needs.

The matrix may be used to at least partially coat any number ofcontinuous reinforcements (e.g., separate fibers, tows, rovings, socks,and/or sheets of continuous material) and, together with thereinforcements, make up a portion (e.g., a wall) of composite structure12. The reinforcements may be stored within or otherwise passed throughhead 16. When multiple reinforcements are simultaneously used, thereinforcements may be of the same material composition and have the samesizing and cross-sectional shape (e.g., circular, square, rectangular,etc.), or a different material composition with different sizing and/orcross-sectional shapes. The reinforcements may include, for example,carbon fibers, vegetable fibers, wood fibers, mineral fibers, glassfibers, plastic fibers, metallic wires, optical tubes, etc. It should benoted that the term “reinforcement” is meant to encompass bothstructural and non-structural (e.g., functional) types of continuousmaterials that are at least partially encased in the matrix dischargingfrom head 16.

The reinforcements may be exposed to (e.g., at least partially coatedwith) the matrix while the reinforcements are inside head 16, while thereinforcements are being passed to head 16, and/or while thereinforcements are discharging from head 16. The matrix, dry (e.g.,unimpregnated) reinforcements, and/or reinforcements that are alreadyexposed to the matrix (e.g., pre-impregnated reinforcements) may betransported into head 16 in any manner apparent to one skilled in theart. In some embodiments, a filler material (e.g., chopped fibers, nanoparticles or tubes, etc.) may be mixed with the matrix before and/orafter the matrix coats the continuous reinforcements.

One or more cure enhancers (e.g., a UV light, an ultrasonic emitter, alaser, a heater, a catalyst dispenser, etc.) 18 may be mounted proximate(e.g., within, on, and/or adjacent) head 16 and configured to enhance acure rate and/or quality of the matrix as it is discharged from head 16.Cure enhancer 18 may be controlled to selectively expose portions ofstructure 12 to energy (e.g., UV light, electromagnetic radiation,vibrations, heat, a chemical catalyst, etc.) during material dischargeand the formation of structure 12. The energy may trigger a chemicalreaction to occur within the matrix, increase a rate of the chemicalreaction, sinter the matrix, harden the matrix, solidify the matrix,polymerize the matrix, or otherwise cause the matrix to cure as itdischarges from head 16. The amount of energy produced by cure enhancer18 may be sufficient to cure the matrix before structure 12 axiallygrows more than a predetermined length away from head 16. In oneembodiment, structure 12 is completely cured before the axial growthlength becomes equal to an external diameter of the matrix-coatedreinforcement.

The matrix and/or reinforcement may be discharged from head 16 via atleast two different modes of operation. In a first mode of operation,the matrix and/or reinforcement are extruded (e.g., pushed underpressure and/or mechanical force) from head 16 as head 16 is moved bysupport 14 to create features of structure 12. In a second mode ofoperation, at least the reinforcement is pulled from head 16, such thata tensile stress is created in the reinforcement during discharge. Inthis mode of operation, the matrix may cling to the reinforcement andthereby also be pulled from head 16 along with the reinforcement, and/orthe matrix may be discharged from head 16 under pressure along with thepulled reinforcement. In the second mode of operation, where the matrixis being pulled from head 16 with the reinforcement, the resultingtension in the reinforcement may increase a strength of structure 12(e.g., by aligning the reinforcements, inhibiting buckling, etc.) aftercuring of the matrix, while also allowing for a greater length ofunsupported structure 12 to have a straighter trajectory. That is, thetension in the reinforcement remaining after curing of the matrix mayact against the force of gravity (e.g., directly and/or indirectly bycreating moments that oppose gravity) to provide support for structure12.

The reinforcement may be pulled from head 16 as a result of head 16being moved by support 14 away from an anchor point 20. In particular,at the start of structure formation, a length of matrix-impregnatedreinforcement may be pulled and/or pushed from head 16, deposited ontoanchor point 20, and cured, such that the discharged material adheres(or is otherwise coupled) to anchor point 20. Thereafter, head 16 may bemoved away from anchor point 20, and the relative movement may cause thereinforcement to be pulled from head 16. It should be noted that themovement of reinforcement through head 16 could be assisted via internalfeed mechanisms, if desired. However, the discharge rate ofreinforcement from head 16 may primarily be the result of relativemovement between head 16 and anchor point 20, such that tension iscreated within the reinforcement. As discussed above, anchor point 20could be moved away from head 16 instead of or in addition to head 16being moved away from anchor point 20.

As can be seen in FIG. 1, head 16 may include, among other things, anoutlet 22 and a matrix reservoir 24 located upstream of outlet 22. Inthis example, outlet 22 is a single-channel nozzle configured todischarge composite material having a generally circular, tubular, orrectangular cross-section. The configuration of head 16, however, mayallow outlet 22 to be swapped out for another outlet (not shown) thatdischarges composite material having a different shape (e.g., a flat orsheet-like cross-section, a multi-track cross-section, etc.). Fibers,tubes, and/or other reinforcements may pass through matrix reservoir 24and be wetted (e.g., at least partially coated and/or fully saturated)with matrix prior to discharge.

A controller 26 may be provided and communicatively coupled with support14 and head 16. Each controller 26 may embody a single processor ormultiple processors that are programmed and/or otherwise configured tocontrol an operation of system 10. Controller 26 may include one or moregeneral or special purpose processors or microprocessors. Controller 26may further include or be associated with a memory for storing data suchas, for example, design limits, performance characteristics, operationalinstructions, tool paths, and corresponding parameters of each componentof system 10. Various other known circuits may be associated withcontroller 26, including power supply circuitry, signal-conditioningcircuitry, solenoid driver circuitry, communication circuitry, and otherappropriate circuitry. Moreover, controller 26 may be capable ofcommunicating with other components of system 10 via wired and/orwireless transmission.

One or more maps may be stored in the memory of controller 26 and usedduring fabrication of structure 12. Each of these maps may include acollection of data in the form of lookup tables, graphs, and/orequations. In the disclosed embodiment, the maps may be used bycontroller 26 to determine the movements of head 16 required to producedesired geometry (e.g., size, shape, material composition, performanceparameters, and/or contour) of structure 12, and to regulate operationof cure enhancer(s) 18 and/or other related components in coordinationwith the movements.

It has been found that the material discharged by head 16 may havecharacteristics, which are at least partially dependent on how thematerial is processed by head 16. For example, a glass transitiontemperature (Tg) of the material can be affected by a temperatureachieved prior to discharge and/or during curing subsequent to dischargefrom outlet 22. In particular, a higher temperature achieved within thematrix during curing generally results in a higher Tg of the finishedstructure 12. Accordingly, it may be beneficial to selectively increasethe matrix temperature to a level higher than can be achieved solely viacure enhancer(s) 20 and/or resulting normally from chemical reactionsoccurring within the matrix. Care must be taken, however, to avoidpremature curing (e.g., curing prior to discharge from outlet 22) causedby the elevated temperatures and to ensure consistent and even heatingthroughout the matrix.

It has also been found that preheating the matrix (i.e., heating thematrix to an elevated temperature just below a cure initiationtemperature at which molecules begin to cross-bond with each other) mayreduce an amount of energy exposure required outside of head 16 toinitiate and/or complete through-curing of the matrix. This may beparticularly helpful, for example, in applications where it is difficultto fully penetrate the reinforcements (e.g., opaque reinforcements suchas carbon) with the cure energy.

In the embodiment of FIG. 2, the matrix within reservoir 24 or otherwisepassing through head 16 may be selectively preheated prior to discharge,so as to increase the temperature achieved inside the matrix duringcuring. The preheating may be facilitated by way of a heater 40. In thedisclosed example, heater 40 is an electric coil placed in a vicinity ofhead 16 (e.g., wrapped around matrix reservoir 24 and/or outlet 22). Itis contemplated, however, that heater 40 could alternatively be placedinside of head 16 or at some location upstream of head 16. For example,heater 40 could embody a cartridge heater embedded within a wall ofmatrix reservoir 24 and/or outlet 22, or an electrode heater in directfluid contact with the matrix (e.g., inside of reservoir 24). Otherheater configurations are also contemplated.

Heater 40 may be regulated (e.g., selectively energized by controller26) to increase the temperature of the matrix inside head 16 to about80-95% of a threshold temperature that initiates or otherwise causescuring of the matrix (e.g., the “kick-off” temperature). With thispreheating, cure enhancers 18 may more easily trigger cure initiationafter discharge (e.g., via additional direct heating and/or via UVreactions that cause further heating), and the matrix temperatureachieved during the reaction may be higher than otherwise possible. Itis contemplated that the kickoff temperature of a particular matrixcould be selectively lowered (e.g., via one or more thermal initiators),in addition to preheating the matrix, such that an even lower level ofenergy exposure from cure enhancer(s) 18 may be required.

In the embodiment of FIG. 2, one or more portions of head 16 may beprovided with an insulating jacket 42. Jacket 42 may embody any type ofinsulating layer or material applied to any portion of head 16, with theprimary purpose being to reduce heat transfer with (e.g., loss to) theenvironment (and/or other portions of head 16) and thereby facilitategreater accuracy in matrix temperature control. It is contemplated thata sensor 44 could be associated with reservoir 24, if desired, and usedto provide feedback control signals associated with the matrixtemperature. Controller 26 may be configured to receive these signalsand responsively adjust current levels passing through heater 40 aloneand/or in combination with adjustments to operation of cure enhancer(s)18.

FIG. 3 is a flowchart depicting an exemplary method that may beimplemented by system 10 and regulated by controller 26 duringfabrication of structure 12. FIG. 3 will be discussed in more detail inthe following section to further illustrate the disclosed concepts.

INDUSTRIAL APPLICABILITY

The disclosed system may be used to manufacture composite structureshaving any desired cross-sectional shape and length. The compositestructures may include any number of different fibers of the same ordifferent types and of the same or different diameters, and any numberof different matrixes of the same or different makeup. Operation ofsystem 10 will now be described in detail.

At a start of a manufacturing event, information regarding a desiredstructure 12 may be loaded into system 10 (e.g., into controller 26 thatis responsible for regulating operations of support 14 and/or head 16)(Step 300). This information may include, among other things, a size(e.g., diameter, wall thickness, length, etc.), a contour (e.g., atrajectory), surface features (e.g., ridge size, location, thickness,length; flange size, location, thickness, length; etc.), connectiongeometry (e.g., locations and sizes of couplings, tees, splices, etc.),reinforcement selection, matrix selection, etc. It should be noted thatthis information may alternatively or additionally be loaded into system10 at different times and/or continuously during the manufacturingevent, if desired. Based on the component information, one or moredifferent reinforcements and/or matrix materials may be installed and/orcontinuously supplied into system 10.

To install the reinforcements, individual fibers, tows, and/or ribbonsmay be passed through matrix reservoir 24 and outlet 22. In someembodiments, the reinforcements may also need to be connected to apulling machine (not shown) and/or to a mounting fixture (e.g., toanchor point 20). Installation of the matrix material may includefilling head 16 (e.g., reservoir 24) and/or coupling of an extruder (notshown) to head 16.

At the same time as or after completion of Step 300, controller 26 (or asoftware module that forms a portion of system 10) may receive and/ordetermine operational properties of the selected matrix (Step 310).These properties may include, among other things, a desired glasstransition temperature for structure 12 and/or a temperature that shouldbe achieved within head 16 via heater 40 alone and/or a temperatureachieved during curing via a combination of heater 40 and cureenhancer(s) 18 that will produce the desired glass transitiontemperature. These properties may be stored, for example, within thememory of controller 26 as one or more relationship maps that can bereferenced by controller 26 during operation of system 10.

After completion of Steps 300 and 310, controller 26 may monitor atemperature of the matrix (Step 320), and determine if the temperatureis within a desired range suitable for material discharge from head 16(Step 330). This temperature may include the temperature of matrixwithin head 16 induced by heater 40 alone or a maximum temperature ofthe matrix achieved via energy received from both heater 40 and cureenhancer(s) 18. In one embodiment, the temperature of the matrix may bedetermined, at least in part, based on signals generated by sensor 44.For example, the temperature may correspond directly to the signals.Alternatively, the temperature may correspond to an amount of energyexposure from heater 40 and/or cure enhancer(s) 18, as indicated bylevels of current supplied to these devices and regulated by controller26.

When the temperature is within the desired range (Step 330: Y),controller 26 may initiate discharge of material from head 16 and thefabrication of structure 12 (Step 340). For example, the reinforcementsmay be pulled and/or pushed along with the matrix material from head 16.Support 14 may also selectively move head 16 and/or anchor point 20 in adesired manner, such that an axis of the resulting structure 12 followsa desired three-dimensional trajectory.

However, when controller 26 determines at Step 330 that the temperatureof the matrix is not within the desired range (Step 330: N), controller26 may selectively adjust operation of heater 40 and/or cure enhancer(s)18 to bring the matrix temperature into the desired range (Step 350).The desired range may include, for example about (e.g., withinengineering tolerances) 80-95% of the kickoff temperature (e.g., thetemperature at which self-supported curing occurs) of the matrix.Control may then return to Step 320.

Controller 26 may periodically or continuously monitor and selectivelyadjust the matrix temperature during fabrication of structure 12. Oncestructure 12 has grown to a desired length, structure 12 may be severedfrom system 10.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the disclosed system. Otherembodiments will be apparent to those skilled in the art fromconsideration of the specification and practice of the disclosed system.It is intended that the specification and examples be considered asexemplary only, with a true scope being indicated by the followingclaims and their equivalents.

What is claimed is:
 1. An additive manufacturing system, comprising: asupport; a print head operatively connected to and moveable by thesupport, the print head configured to discharge a continuousreinforcement that is at least partially coated in a liquid matrix; acure enhancer connected to the print head and configured to expose thedischarge to cure energy to cause the liquid matrix to at leastpartially polymerize; a heater configured to warm the liquid matrixinside of the print head; and a controller in communication with theheater and the cure enhancer, the controller being configured toselectively activate the heater and the cure enhancer.
 2. The additivemanufacturing system of claim 1, wherein the controller is configured toselectively activate at least one of the heater and the cure enhancerbased on a desired glass transition temperature of the liquid matrixwithin a fabricated structure.
 3. The additive manufacturing system ofclaim 2, further including a sensor configured to generate a signalindicative of a temperature of the liquid matrix inside of the printhead, wherein the controller is configured to activate the at least oneof the heater and the cure enhancer based on the signal.
 4. The additivemanufacturing system of claim 1, further including an insulating jacketassociated with the print head to reduce heat loss from the liquidmatrix.
 5. The additive manufacturing system of claim 3, wherein thecontroller is configured to cause the print head to discharge materialonly when the signal indicates an internal temperature of the liquidmatrix within a desired range.
 6. A method of additively manufacturing acomposite structure, comprising: receiving a liquid matrix into a printhead; receiving a continuous reinforcement into the print head; at leastpartially coating the continuous reinforcement with the liquid matrixinside of the print head; and selectively discharging the continuousreinforcement and the liquid matrix only when a temperature of theliquid matrix is within a desired range.
 7. The method of claim 6,further including generating a signal indicative of the temperature ofthe liquid matrix, wherein selectively discharging the continuousreinforcement and the liquid matrix includes selectively discharging thecontinuous reinforcement and the liquid matrix only when the signalindicates that the temperature of the liquid matrix is within thedesired range.
 8. The method of claim 6, further including selectivelyconditioning the liquid matrix when the temperature of the liquid matrixis outside of the desired range.
 9. The method of claim 8, whereinselectively conditioning includes heating the liquid matrix inside ofthe print head.
 10. The method of claim 9, further including exposingthe liquid matrix to a cure energy after discharge from the print head.11. The method of claim 10, wherein selectively conditioning furtherincludes adjusting an amount of energy directed to the liquid matrixafter discharge from the print head.
 12. The method of claim 9, whereinheating the liquid matrix includes heating the liquid matrix to about80-95% of a kickoff temperature of the liquid matrix.
 13. The method ofclaim 9, wherein heating the liquid matrix inside of the print headincreases a glass transition temperature of the composite structure. 14.The method of claim 6, wherein the desired range is specific to theliquid matrix.
 15. A method of additively manufacturing a compositestructure, comprising: receiving a liquid matrix into a print head;receiving a continuous reinforcement into the print head; at leastpartially coating the continuous reinforcement with the liquid matrixinside of the print head; monitoring a temperature of the liquid matrixinside of the print head; responsively adjusting the temperature of theliquid matrix; selectively discharging the continuous reinforcement andthe liquid matrix when a temperature of the liquid matrix is within adesired range; and exposing the liquid matrix to a cure energy afterdischarge.
 16. The method of claim 15, further including generating asignal indicative of the temperature of the liquid matrix, whereinselectively discharging the continuous reinforcement and the liquidmatrix includes selectively discharging the continuous reinforcement andthe liquid matrix only when the signal indicates that the temperature ofthe liquid matrix is within the desired range.
 17. The method of claim15, wherein selectively conditioning includes heating the liquid matrixinside of the print head.
 18. The method of claim 17, whereinselectively conditioning further includes adjusting the exposing of theliquid matrix to energy after discharge from the print head.
 19. Themethod of claim 18, wherein heating the liquid matrix includes heatingthe liquid matrix to 80-95% of a kickoff temperature of the liquidmatrix.
 20. The method of claim 19, wherein heating the liquid matrixinside of the print head increases a glass transition temperature of thecomposite structure.